Pages

Tuesday, June 25, 2013

Seriously! This is one of the top images that comes up in a Google search for "brooding"

I meant Brooding juveniles like THIS!

from the Smithsonian NMNH USARP

In other words, these are "baby" starfish that are cared for by the mother until they are ready to head off ont their own. Parental investment resulting in a succesful offspring.

Sometimes starfish (and indeed most echinoderms) can appear kind of alien. No head. Mouth on the bottom. 5 part radial symmetry. Strange adaptations. All kind of weird sometimes.

So, I suppose its appropriate that the WEIRDEST of ALL echinoderm (and starfish) behavior is that starfish have this almost mammal-like (or at least, vertebrate like) behavior!! Some starfish species will actually brood and carry little starfish just like the cutest little furry thing you can think of!

But many starfish species stray from that typical cycle, and somewhere between the time the sperm fertilize the eggs and the settled "babies" are established the whole life cycle CHANGES to give you this:

Yes. Tiny baby or small juvenile starfish which are held by the mother around the mouth! (this varies as we'll see). Why do some starfish do this? And not the more 'typical' behavior?

Scientists have known about brooding behavior in several species of starfish since the 19th Century but only recently has there been the extensive observation and insight to finally piece together the complete story!

Hamel and Mercier's paper exhaustively studies L. polaris' complete reproductive cycle, which pretty thoroughly documents the reproductive behavior in this species. Bear in mind, that this starfish has been known since 1842 and yet our knowledge of its reproduction has only come to us recently (published in 1995)!

Information on brooding remains of interest-but the behavior and its evolution is poorly understood.

1.PSEUDOCOPULATION

Figure 1 from Hamel & Mercier 1995

As a prelude to the actual spawning there are massive aggregations of these animals. They're involved in an unusual behavior known as pseudocopulation. There's no penetration or combination of sexual organs, nor is there any actual spawning. The animals all just get together into a big pile. Sort of preparation for the main event.

Bear in mind, OTHER than during mating season (November to February), these animals all typically ignore or even avoid one another.

Many echinoderm species practice pseudocopulation which I've written about here. Its not always clear why different species pseudocopulate. But one thing seems clear: It helps the chances of their sperm and eggs get together.

Here (from Figure 5 in Mercier & Hamel) we see a close up of eggs UNDER the female in C. Which then grow up into the cute as the dickens starfish in D. Growth was after about 5 and half months.

4. After fertilization, development proceeds. Here's a summary panel of the different stages. The top row is the developing embryo. It continues through different stages until it reaches "J."

At that point the animal is practically ready to move off on its own..

Figure 9 showing development from embryos to small starfish

Interestingly, Hamel & Mercer found that the development proceeded on its own if the embryos were unbrooded. They suggest that brooding is behavior which protects the embryos/juvenile starfish from debris and other materials. Animals observed in the field were clear of excess materials.

Protection was also a likely consideration since unprotected embryos/juvenile starfish were rapidly devoured by sea urchins or other grazing animals if they were not protected by the adult.

The whole cycle is sumarized in this convenient cartoon!

Figure 4 from Hamel & Mercier 1995

There were MANY more details! If the topic of brooding interests you I urge you to check it out!

BUT That's NOT the end of it!

5. Brooding is diverse. SEVERAL different species of sea stars brood. Almost all of them are either cold-water species, living in the deep-sea or at the poles. Sometimes brooding is in temperate water species.. But typically not in the tropics.

Brooding also takes different forms. The oral 'mouth' or gastric brooding mode is but one kind. Here is Diplasterias from the Antarctic! MANY starfish in the Antarctic brood juvenile starfish!

Recent research has brought a powerful spotlight on not just the ecological, but the overall, importance of sea cucumbers to the environment. Sea cucumbers occur all over the world and at all depths. Often, when present, they are abundant or at least a significant part of the fauna present.

But the key dynamic present to their importance is that they cycle or process what they eat and what they defecate contributes to the health of the habitat they inhabit.

I realize that articles about "coral reefs saved by sea cucumber poop" sound kind of silly on the surface, but read and understand below.... (note also the Journal of Geophysical Research? Important stuff gets put in there.)

Coral has to develop or accumulate calcium carbonate, which is the mineral used to compose coral skeletons, at an equal or better than the rate at which the coral loses calcium carbonate via erosion, natural dissolution, etc.

A survey of the sea cucumbers Stichopus herrmanni and Holothuria lecuospilota in One Tree Reef, Australia showed that the sea cucumbers could digest and dissolve so much of the adjoining sediment and rubble (ie the sand) that they actually contributed up to 50% or MORE of the total amount calcium carbonate dissolved over a night time. Presumably this was made available for coral to use for reef development.

Chemically, calcium carbonate is very alkaline or basic. So, sort of like an antacid. What do you do when you have stomach acids that are misbehaving? Drop some of those tablets to "cancel" out the acidity.

So, sea cucumbers contribute calcium carbonate to the coral reef's "chemical budget". They act like a natural antacid to neutralize other acidic environmental sources. Under normal conditions, there's an equilibirum. The abundance or number of sea cucumbers can affect this.Thus, in theory, MORE sea cucumbers might produce so MUCH alkalinity (or "basic" poop to the water) that conceivably they could function as a control or at least a buffer against increases in more acidic sea water. This obviously is important when you consider ocean acidification resulting from global warming. Sea cucumber poop is an important part of helping to keep the geochemical balance of a coral reef in equilibrium.

2. Sea Cucumbers EAT tasty bottom poop and clean it up!
Poop is processed into useful nutrients! Over abundance of nutrients (i.e eutrophication) is broken up by sea cucumber feeding!

MacTavish and his colleagues studied a nutrient-rich environment covered by algae, mussel feces and other nutirent-rich goodies. Under normal circumstances, these would build up bacteria, ammonia and other factors creating conditions that contribute to the growth of algae, which ultimately chokes everything else out (aka eutrophication).

But you put a sea cucumber into these settings? They LOVE it! They eat and all sorts of good things happen:

Bacterial abundance increases

Organic material (i.e., the goo) begins to decompose more quickly

Organic materials are redistributed from the marine sediments into the water

Sea cucumbers help to break down organic material and redistribute the nutrients! The poop is an important part of that process.

Eutrophication-the overabundance of nutrients resulting in undesirable growth of algae and hypoxia-is a common problem in aquacutlure ponds.

Image by Smartfish-ioc

But putting a sea cucumber into the mix? A critter that LOVES organic nutrients and gooey stuff like that? It would go to town! Cleaning up the bottom and cycling those bottom nutrients... Seems like a win-win solution for cleaning up the bottom of say a fish or mussel farm where feces from the animals accumulate in huge amounts.

So yes. Sometimes sea cucumbers eat poop. And then poop poop, which is probably "cleaner" than what went in the first place...

4. Sea Cucumber poop is good for plants (mangroves, seagrass, etc.), which are part of a healthy ecosystem

Image by Eunice Khoo- "Mermate"

So, by this I don't just mean ONLY the poop-but the animal digesting and then processing the sediment. This follows everything from the above-they break down organic detritus and make the nutrients available to the water column preventing hypoxia and other bad things going down in the sediment...

Think of them as earthworms! go through the bottom sediments, eat all the organics and leave the sediment.. that's sea cucumber poop!

5. Deep-Sea Cukes have pretty diverse microbial faunas that live in their guts! (and thus their poop!)
Deep-sea sea cucumbers perform very much the same kind of function as the shallow water ones. They live in much finer mud and are often rained upon by nutrients from the surface. Many of these critters, such as Molpadia (shown here) live buried in the mud.

Shallow water echinothurioid urchins are "proper" fire urchins. As opposed to these other "fire colored" spiny urchins, such as Astropyga which are diadematoid urchins. A completely different group!!

"Spiny" urchins are distinguished by the presence of an Anal Cone. See that white bulb on top? THAT is where the poop comes out! You don't see that in "proper" fire urchins as we'll be seeing.. Note also that the spines are much longer.

And if its not clear by now, YES. They're pretty damn venomous. My understanding is that its very painful.. but typically not lethal.

and they certainly do seem like they do, don't they??

Image by Bruce Magun

Image by Daniel Stassen

Close ups! showing some of the brillaint colors, spine patterns and etc.. I suspect most of these are Asthenosoma varium

Image by MerMate

Image by Daphna130

Image by lupopeye

Image by maractwin

Image by Nick Hobgood

Image by B. Maither

Image by Russell Taylor

Here's some differing species from around the Indo-Pacific

From the Red Sea, Asthenosoma marisrubi with a more mellow look...

Image by Key of Life

Here are the spines..still basically the same but different color and slightly different shape..

Image by Le Congre

Asthenosoma spp. showing many different colors...

Image by S1mon Mar5h

Image by Clark Chang

Image by Jesse Claggett

Image by Richard Barnett

What's even MORE interesting? These urchins have tiny critters which live as commensals(?) among the highly poisonous spines! (this neat vid also shows a LOT of close up details)Urchin Riders from liquidguru on Vimeo.
Some of the little buggers actually "hollow" out a space, clearing out spines where they can live! You can see the bare patch on this one...

Image by Klaus Stiefel

In addition to all the various crustaceans, Amazingly. Here is a benthic ctenophore (which I've written about here) ON A FIRE URCHIN!! (the white blobby bits are the feeding tentacles) Mind. blown!! and incidentally.. a likely first occurrence recorded....

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
Need to hire an invertebrate zoologist/marine biologist? Please contact me!